The New York Times did an article back in February about how Avatar in 3D caused symptoms of motion sickness is many viewers. The explanation given was that 3D films cause the viewer's eyes to make unnatural movements which become stressful after a period of time.
Perhaps different people are more or less susceptible to this effect, as seems to be the case with reading in a moving car -- that activity never bothers me, but I have known many people who can't do it for long without feeling sick.
This issue is definitely something that 3D TV hardware vendors and content creators should be concerned with as they roll out this next-big-thing in TV entertainment.

Could it possibly be an attempt to delay an emerging market that Samsung entered early, with a poorly performing implementation? All reviewers of the Samsung LCD 3D TV product have complained about L/R eye view crosstalk.

Colin, I think your drawing a parallel to the experience of early days of VR is very astute and interesting.
But I also think that we may be missing a point if we just dwell on the hardware side of the issue. A lot can be done when one is creating 3-D content and post processing it -- in order to prevent the potential 3-D disastar, according to Insight Media's Chris Chinnock.
See the follow-up story at:
http://www.eetimes.com/showArticle.jhtml?articleID=224500003

Samsung's health hazard warning reminds me of the fledgling virtual reality (VR) market of the late 1980s that consumers revolted against after medical experts hinted that head-mounted displays (HMDs) could encourage "lazy eye" in youngsters. Wearing 3D glasses is not as invasive as an HMD, but the old "lazy eye" scare is at least one reason that 3D TV vendors still warn adults today that their kids are at the most risk. Regarding the 3D movie craze, I have several friends who have been made nauseous by watching a 3D movie at the cinema--that's after just two hours viewing. With 3D TVs in the home, there is no way to regulate how much or under what conditions people watch. I suggest that 3D TV vendors start preparing their defense against lawsuits alleging all sorts of aches, pains and worse, caused by 3D TV. I suspect that legal prep-work against such lawsuits is Samsung's reason for posting this health warning at this time.